(named after the city of Lölling in Austria), a mineral of the arsenide class. Its composition is FeAs2, with 27.18 percent Fe and 72.82 percent As; admixtures of S, Sb, Co, and Ni are common. Loellingite crystallizes in the orthorhombic system, forming prismatic crystals. With a crystal structure resembling that of marcasite, loellingite generally occurs in solid granular masses. Its color ranges from silver-white to steel-gray. Loellingite has a hardness of 5–5.5 on Mohs’ scale and a density of 7,000–7,400 kg/m³. It decomposes upon heating at temperatures above 4000°C with the precipitation of arsenic and exhibits good electrical conductivity. It is a rare mineral, occurring in hydrothermal and contact-metasomatic deposits. In the USSR deposits are found in the Urals, Middle Asia, and Western and Eastern Siberia. Major deposits are also found in Norway and Canada. As an iron arsenide with the highest arsenic content, loellingite is an arsenic ore.